1. Field of the Invention
The present disclosure relates to an organic light emitting display device and a method of manufacturing the same, and particularly, to an organic light emitting display device having a color filter on thin film transistor (TFT) (COT) structure.
2. Discussion of the Related Art
Recently, as an interest in information displays has been on the rise and demand for using portable information mediums has grown, research into and commercialization of lighter, thinner flat panel displays (FPDs), replacing cathode ray tubes (CRTs), existing displays, has been actively conducted.
In the flat panel display field, liquid crystal displays (LCDs) have come to prominence. However, since LCDs are light receiving devices, rather than light emitting devices, and have shortcomings in terms of brightness, a contrast ratio, a viewing angle, and the like, novel display devices that may be able to overcome such shortcomings have been actively developed.
An organic light emitting display device, one of novel display devices, is self-luminous and thus it is excellent in terms of a viewing angle and a contrast ratio. Also, since the organic light emitting display device does not require a backlight, the organic light emitting display device may be lighter and thinner and is advantageous in terms of power consumption. In addition, the organic light emitting display device may be driven with a low DC voltage and have a fast response speed.
Hereinafter, a basic structure and operational characteristics of an organic light emitting display device will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a light emitting principle of a general organic light emitting diode.
In general, an organic light emitting display device includes an organic light emitting diode (OLED) as illustrated in FIG. 1.
The OLED includes an anode 18 as a pixel electrode, a cathode 28 as a common electrode 28, and organic layers 30a, 30b, 30c, 30d, and 30e formed between the anode 18 and the cathode 28.
The organic layers 30a, 30b, 30c, 30d, and 30e include a hole transport layer (HTL) 30b, an electron transport layer (ETL) 30d, and an emission layer (EML) 30c interposed between the hole transport layer 30b and the electron transport layer 30d. 
Here, in order to enhance luminous efficiency, a hole injection layer (HIL) 30a is interposed between the anode 18 and the hole transport layer 30b and an electron injection layer (EIL) 30e is interposed between the cathode 28 and the electron transport layer 30d. 
In the OLED configured in such a manner, when a positive (+) voltage and a negative (−) voltage are applied to the anode 18 and the cathode 28, respectively, holes passing through the hole transport layer 30b and electrons passing through the electron transport layer 30d are transferred to the emission layer 30c to form excitons, and when the excitons transition from an excited state to a ground state, namely, a stable state, light is generated.
In the organic light emitting display device, sub-pixels each including the OLED having the foregoing structure are arranged in a matrix form and selectively controlled with a data voltage and a scan voltage to display an image.
Here, the organic light emitting display device is divided into a passive matrix organic light emitting display device and an active matrix type organic light emitting display device using a thin film transistor (TFT) as a switching element. Here, in the active matrix type organic light emitting display device, a TFT, an active element, is selectively turned on to select a sub-pixel and light emission of the sub-pixel is maintained with a voltage maintained in a storage capacitor.
FIG. 2 is a cross-sectional view schematically illustrating a structure of a general organic light emitting display device.
Referring to FIG. 2, the general organic light emitting display device includes a substrate 1 in which a pixel part and a TFT pad part are defined, and an encapsulating layer 10 formed on the substrate 1 and covering the pixel part.
A polarizing plate (not shown) for presenting reflection of light incident from the outside may be attached to the encapsulating layer 10 through an adhesive layer.
Although not shown, pixels are disposed in a matrix form in the pixel part of the substrate 1, and driving elements such as a scan driver or a data driver for driving the pixels, and other components are positioned on outer side of the pixel part.
Pad electrodes for transmitting an electric signal to the scan driver and the data driver are positioned in the TFT pad part of the substrate 1.
The encapsulating layer 10 is formed above the OLEDs 30 and the driving circuits formed on the substrate 1 to seal and protect the OELDs 30 and the driving circuits from the outside.
Referring to the encapsulating layer 10, in detail, a first protective layer 13a, an organic layer 13b, and a second protective layer 13c are sequentially formed as an encapsulating unit on the substrate 1 with the cathode 28 formed thereon.
A protective film 15 formed of a plurality layers is positioned to face the entire surface of the substrate 1 with the second protective layer 13c formed thereon for encapsulation, and an adhesive 14 which is optically transparent and has adhesive properties is installed between the substrate 1 and the protective film 15.
In the general organic light emitting display device configured in such a manner, when an organic light emitting layer emitting white light is used, color filters are used to change white light to red, green, and blue light.
In manufacturing the organic light emitting display device having the COT structure (color filter on TFT), at least twelve masks are required to form a light blocking layer, an active layer, a gate line, a contact hole, a data line, a color filter, an overcoat layer, a protective layer, a pixel electrode, and a bank.
Thus, efforts to reduce the number of masks in terms of productivity have been made.